CARNOT BATTERY AND ENERGY STORAGE SYSTEM

Description

TECHNICAL FIELD

The present invention relates to a Carnot battery and an energy storage system.

BACKGROUND ART

In recent years, energy storage technologies have been attracting attention to equalize grid power including electric power that is derived from renewable energy with large output fluctuation. Pumped-storage hydroelectricity, lithium-ion batteries, compressed air energy storage (CAES), and hydrogen storage are known as the energy storage technologies. However, these technologies have problems in location requirements, cost, and storage duration, and new energy storage technologies are thus being developed. As an example of the new energy storage technologies, Carnot batteries that accumulate energy in heat have been attracting attention. For example, Patent Literature 1 discloses a Carnot battery that uses sensible heat of solid particles, such as concrete, gravel, and rock, to accumulate heat and then uses the accumulated heat to generate electricity.

Citation List

Patent Literature

• • Patent Literature 1: Unexamined Japanese Patent Application Publication (Translation of PCT Application) No. 2022-502623

SUMMARY OF INVENTION

Technical Problem

Since the Carnot battery of Patent Literature 1 uses the sensible heat for heat accumulation with the solid particles, storage of a large amount of the heated solid particles in a silo is required to keep air supplied to a turbine at a high temperature. Thus, in the Carnot battery of Patent Literature 1, heat is accumulated in the solid particles by a heater and stored in the silo during times of low power demand, and the stored solid particles are transferred to a heat exchanger to generate electric power during other times of high power demand. As described above, the Carnot battery of Patent Literature 1 cannot stably supply electric power to the outside, and thus has a room for improvement.

The present invention is made in view of the above circumstance, and an objective of the present invention is to provide a Carnot battery and an energy storage system capable of stably supplying electric power of which output fluctuation derived from renewable energy is absorbed.

Solution to Problem

In order to achieve the above objective, the Carnot battery according to the present disclosure includes:

• • first conversion means for converting electric power into heat to generate hot air;
  • a high-temperature heat accumulator disposed downstream of the first conversion means and including a phase change material, the phase change material being configured to receive hot air supplied by the first conversion means to accumulate and dissipate heat; and
  • second conversion means for collecting heat from hot air supplied by the high-temperature heat accumulator to convert the heat into electric power, the second conversion means being disposed downstream of the high-temperature heat accumulator.

Advantageous Effects of Invention

The present invention can provide a Carnot battery and an energy storage system capable of stably supplying electric power of which output fluctuation derived from renewable energy is absorbed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a configuration of an energy storage system according to an embodiment of the present invention;

FIG. 2 illustrates a configuration of a Carnot battery according to the embodiment of the present invention;

FIG. 3 is a cross-sectional view illustrating configurations of an electric heater and a high-temperature heat accumulator according to the embodiment of the present invention;

FIG. 4A is an enlarged front view of a part of the high-temperature heat accumulator according to the embodiment of the present invention;

FIG. 4B is a cross-sectional view of the high-temperature heat accumulator taken along the line A-A of FIG. 4A;

FIG. 5 is a cross-sectional view illustrating a configuration of a low-temperature heat accumulator according to the embodiment of the present invention;

FIG. 6 illustrates a cycle of a phase transition of a phase change material according to the embodiment of the present invention;

FIG. 7 is a schematic diagram illustrating a configuration of a heat supply system according to the embodiment of the present invention;

FIG. 8 is a cross-sectional view illustrating a configuration of a melter according to the embodiment of the present invention;

FIG. 9 is a cross-sectional view illustrating a configuration of a dissipated-heat collector according to the embodiment of the present invention;

FIG. 10 is a flowchart illustrating procedures of a heat supply method according to the embodiment of the present invention; and

FIG. 11 is a cross-sectional view illustrating a configuration of a low-temperature heat accumulator according to a modified example of the present invention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a Carnot battery and an energy storage system according to an embodiment of the present invention are described in detail with reference to the drawings. In the drawings, the same reference sign is assigned to the same or equivalent parts.

The energy storage system according to the embodiment is a system that converts, using a high-temperature heat accumulation material, grid power with large output fluctuation into stable generated power with small output fluctuation, and collects, using a low-temperature heat accumulation material, heat generated in the conversion of grid power into generated power, to supply heat to heat-demanding areas. In heat supply, hot water is supplied to consumers through pipes, and the consumers uses the hot water for hot water supply, heating, snow melting, and other purposes.

The high-temperature heat accumulation material and the low-temperature heat accumulation material are both phase change materials (PCMs) that accumulate heat using latent heat. The PCMs absorb or dissipate heat using latent heat resulting from phase change between liquid and solid, and thus have a higher heat accumulation density than sensible heat accumulation materials. The melting point of the high-temperature heat accumulation material is, for example, in the range of 500° C. to 700° C. The high-temperature heat accumulation material dissipates hot air in the range of 500° C. to 700° C. The melting point of the low-temperature heat accumulation material is lower than that of the high-temperature heat accumulation material, and is in the range of 100° C. to 200° C., for example. The low-temperature heat accumulation material supplies, for example, hot water in the range of 70° C. to 80° C. during heat dissipation.

The grid power is electric power supplied by a grid power supply, and may include variable power derived from renewable energy. Electric power derived from renewable energy is, for example, electric power generated by wind power generation, solar power generation, or tidal power generation, and the power generation amount thereof depends on external conditions such as weather, season, and time of day. Hereinafter, it is assumed that grid power includes variable power derived from renewable energy, and short-period fluctuation occurs in the grid power. The short-period fluctuation is fluctuation that has a period of 20 minutes or less and occurs in the amount of electric power.

As illustrated in FIG. 1, an energy storage system 1 includes a Carnot battery 10 that converts grid power with large output fluctuation into stable generated power with small output fluctuation, and a heat supply system 20 that collects heat discharged by the Carnot battery 10 and supplies the heat to heat-demanding areas. The heat supply system 20 collects, for example, heat included in exhaust generated when the Carnot battery 10 converts heat into electric power.

The Carnot battery 10 includes a heat source device 11 that converts grid power into heat, a high-temperature heat accumulator 12 that accumulates and dissipates the heat generated by the heat source device 11, and a steam power generation plant 13 that generates steam using the heat dissipated by the high-temperature heat accumulator 12 to generate electric power. The heat source device 11 is an example of first conversion means for converting electric power into heat to generate hot air. The steam power generation plant 13 is an example of second conversion means for collecting heat from hot air supplied by a high-temperature heat accumulator to convert the heat into electric power.

The heat supply system 20 includes a low-temperature heat accumulator 21 that is configured to be attachable to and detachable from the steam power generation plant 13 and collects and accumulates heat discharged by the steam power generation plant 13, and a dissipated-heat collector 22 that is configured to be able to dispose the low-temperature heat accumulator 21 therein and collects heat dissipated by the low-temperature heat accumulator 21 to supply heat to heat-demanding areas. The heat supply system 20 may use multiple low-temperature heat accumulators 21 sequentially or simultaneously to collect heat from the steam power generation plant 13 and dissipate heat in the dissipated-heat collector 22.

The low-temperature heat accumulator 21 is transportation means, for example, a cartridge that is configured to be transportable by a truck. The low-temperature heat accumulator 21 is transported to heat-demanding areas, and can supply heat in a state where the low-temperature heat accumulator 21 is disposed in the dissipated-heat collector 22. As an example, a configuration may be provided in which the low-temperature heat accumulator 21 accumulates and stores heat during a summer period in which heat accumulation is easier, and then is disposed in the dissipated-heat collector 22 to supply heat using heat dissipated by the low-temperature heat accumulator 21 during a winter period in which heat demand increases.

Next, the components of the Carnot battery 10 according to the embodiment are described. As illustrated in FIG. 2, the heat source device 11 includes an electric heater 11a that generates thermal energy from electric power, and a blower 11b that blows air toward the electric heater 11a to generate breeze of hot air. The electric heater 11a includes a resistance heating element that generates thermal energy through the Joule effect, for example. As long as grid power is supplied, the heat source device 11 receives the grid power to convert the grid power into heat, and continues to supply the heat to the high-temperature heat accumulator 12.

The high-temperature heat accumulator 12 includes a PCM with a large heat capacity, and is disposed downstream of the heat source device 11. The high-temperature heat accumulator 12 receives hot air supplied by the heat source device 11 to accumulate heat, and dissipates the heat toward the surrounding hot air as long as the heat is accumulated. That is, as long as the heat is accumulated, the high-temperature heat accumulator 12 adjusts the temperature of the hot air flowing from the heat source device 11 to be constant.

The melting point of the PCM of the high-temperature heat accumulator 12 is, for example, 570° C. The temperature of hot air dissipated by the high-temperature heat accumulator 12 is in the range of 570° C. to 600° C. A large heat dissipation response occurs when the PCM is solidified, and the heat generation amount is controlled to be constant even when grid power decreases. This maintains inertial force. Thus, the high-temperature heat accumulator 12 preferably accumulates and dissipates heat with the PCM molten inside a covering member.

As illustrated in FIG. 3, the heat source device 11 and the high-temperature heat accumulator 12 are disposed in a pipe 14, for example. The high-temperature heat accumulator 12 is formed such that multiple passages through which air can pass are adjacent to each other and extend in the same direction. The hot air blown by the blower 11b passes through the passages, and each of the passages exchanges heat with a wall surface. The high-temperature heat accumulator 12 may have a honeycomb structure with regular hexagonal holes or a checker brick structure with circular holes, for example.

As illustrated in FIGS. 4A and 4B, the high-temperature heat accumulator 12 is formed by combining a large number of PCM capsules 12A. Each of the PCM capsules 12A is formed as a sphere with a diameter of about 5 mm to 10 mm, for example, and includes a core that is formed of a PCM and a shell that covers the core.

Taking the melting point of the PCM into consideration, the core is preferably an aluminum alloy, for example, an Al—Si alloy (4000 series) with silicon added to aluminum. The Al—Si alloy is, for example, an aluminum alloy with 12% by weight of silicon added to aluminum.

The shell is an example of the covering member that covers the PCM. The shell is preferably a ceramic material, for example, alumina (Al₂O₃) obtained by oxidizing an aluminum alloy. The shell of each PCM capsule 12A is formed of heat-resistant ceramics. This can prevent the core in a molten state from leaking out due to damage caused by heat or external force.

The heater capacity of the heat source device 11 may be, for example, about three times the average input power from the grid power supply. The heat accumulation capacity of the high-temperature heat accumulator 12 may be, for example, equivalent to the amount of electric power used for 12 hours with the average input power from the grid power supply. As an example, assuming that the average input power is 5 MW, the heater capacity of the heat source device 11 is 5 MW×3=15 MW, and assuming that the heat generation efficiency of the heat source device 11 is 100 %, the heat accumulation capacity of the high-temperature heat accumulator 12 is 5 MW×12 hours=60 MWh.

Returning back to FIG. 2, the steam power generation plant 13 includes a steam boiler 13a that generates steam using hot air from the high-temperature heat accumulator 12, a superheater 13b that superheats the steam generated by the steam boiler 13a, a steam turbine 13c that extracts rotational energy from the steam supplied by the superheater 13b, a power generator 13d that generates electric power using the rotational energy from the steam turbine 13c, a condenser 13e that condenses the steam discharged by the steam turbine 13c, and a water supply pump 13f that supplies water condensed by the condenser 13e to the steam boiler 13a. The components of the steam power generation plant 13 are connected in turn via pipes that can supply steam or water, and are configured to circulate the steam or water in the steam power generation plant 13.

The steam boiler 13a takes in the hot air from the high-temperature accumulator 12, and converts the water supplied by the water supply pump 13f into saturated steam. The steam boiler 13a includes a drum that accumulates the water supplied by the water supply pump 13f, and multiple pipes that are disposed in the drum and generate steam through heating of the water in the drum caused by heating air from the high-temperature heat accumulator 12 passing through the pipes. The steam boiler 13a receives hot air in the range of 570° C. to 600° C. from the high-temperature heat accumulator 12, and discharges air at 180° C. as exhaust, for example. This exhaust is used for heat accumulation by the low-temperature heat accumulator 21.

The superheater 13b heats, using the hot air from the high-temperature heat accumulator 12, the saturated steam generated by the steam boiler 13a to be changed to superheated steam.

The steam turbine 13c converts thermal energy of the superheated steam into rotational energy via an impeller and a rotational axis. The rotational axis of the steam turbine 13c is connected to a rotational axis of the power generator 13d, and rotates the rotational axis of the power generator 13d around the axis.

The power generator 13d converts the rotational energy of the steam turbine 13c into electrical energy. When the generated power of the power generator 13d is set to 1 MW, the efficiency of the steam turbine is about 25 %.

The condenser 13e cools and condenses wet steam discharged by the steam turbine 13c, and reduces the exhaust pressure of the steam turbine 13c. A large number of cooling pipes are disposed in a tank of the condenser 13e. The wet steam in the tank can be condensed by causing cooling water to pass through these cooling pipes. At this time, the cooling water having passed through the cooling pipes is changed to hot water, and this hot water can be thus used to supply heat to neighboring sites.

The water supply pump 13f is a pump for supply of water condensed by the condenser 13e to the steam boiler 13a. The components of the Carnot battery 10 are as described above.

Next, the components of the heat supply system 20 according to the embodiment are described. Returning back to FIG. 1. the low-temperature heat accumulator 21 is a moveable cartridge including a PCM that melts at a lower temperature than the PCM of the high-temperature heat accumulator 12. The melting point of the PCM of the low-temperature heat accumulator 21 is, for example, assuming that the temperature of the exhaust from the steam boiler 13a is 180° C., preferably in the range of 140° C. to 160° C., more preferably at 150° C. The low-temperature heat accumulator 21 is changed to a heat accumulation state when the PCM is melted by the exhaust from the steam boiler 13a, and can supply, for example, heat in the range of 70° C. to 80° C. to heat-demanding areas. Hereinafter, the PCM of the low-temperature heat accumulator 21 may be referred to as the “low-temperature PCM” to be distinguished from that of the high-temperature heat accumulator 12.

As illustrated in FIG. 5, the low-temperature heat accumulator 21 includes a large number of PCM capsules 21A, and a container 21B that accommodates the PCM capsules 21A and is formed to allow heat transfer between the PCM capsules 21A and the outside. The low-temperature heat accumulator 21 accumulates, transfers, and dissipates heat of the PCM capsules 21A while the PCM capsules 21A are accommodated in the container 21B. Each of the PCM capsules 21A is formed by encapsulating the low-temperature PCM in an alloy capsule, and has a particle size in the range of 1 mm to 10 mm, for example. The capsule of each PCM capsule 21A is an example of a covering member that covers the low-temperature PCM. The container 21B is formed of a heat transfer material, for example, a metal material. The container 21B is preferably formed in, for example, a cubic shape so as to be stacked on each other. In addition, the container 21B may have a door through which the PCM capsules 21A can be inserted and removed.

As the low-temperature PCM of the low-temperature heat accumulator 21, it is preferable to use a material with the potential to undergo a phase transition from a molten state to a glassy state via a supercooled liquid state when cooled at a certain rate or higher. The supercooled liquid state is a liquid state maintained even when liquid is cooled to the melting point or lower. The glassy state is an amorphous state that occurs at a temperature lower than the glass transition point. The material with the potential to undergo a phase transition to the glassy state can accumulate heat when changing from a crystalline state to the molten state, and then maintain a heat accumulation state by changing to the glassy state. In addition, cold crystallization is induced by temporarily applying heat at the cold crystallization point or higher to the material in the glassy state. This allows dissipation of latent heat.

Specifically, as illustrated in FIG. 6, when cooled from the molten state at the certain rate or higher, the material with the potential to undergo a phase transition to the glassy state undergoes a phase transition to the glassy state at the glass transition point via the supercooled liquid state without dissipating crystallization latent heat. The material in the glassy state is an amorphous solid, and can be thus stored in a stable state for a long period of time while maintaining a heat-accumulated state despite of a low temperature. When a part of the material in the glassy state is heated, the material undergoes a phase transition to the supercooled liquid state at the glass transition point, and further continued heating results in a change to a cold crystalline state at the cold crystallization point. At this time, latent heat is dissipated outside. Crystals obtained by the cold crystallization can be returned to the molten state by heating the crystals to the melting point or higher. The material with the potential to undergo a phase transition to the glassy state can accumulate and dissipate heat through a cycle of the molten state, the supercooled liquid state, the glassy state, the supercooled liquid state, the cold crystallization, and the crystalline state.

The material with the potential to undergo a phase transition to the glassy state is, for example, a polyhydric alcohol, preferably a sugar alcohol. The sugar alcohol is a chain or cyclic polyhydric alcohol in which a carbonyl group of a sugar is reduced. As the sugar alcohol, it is preferable to use a eutectic mixture formed from two or more sugar alcohols, and more preferable to use a ternary sugar alcohol formed from three sugar alcohols, for example. The ternary sugar alcohol is, for example, a eutectic mixture of mannitol, galactitol, and inositol. Adjustment of the composition of this eutectic mixture can vary the melting point, melting latent heat, the cold crystallization point, and cold crystallization latent heat.

The material with the potential to undergo a phase transition to the glassy state has a glass transition point preferably in the range of 10° C. to 50° C., for example, a melting point (a heat accumulation temperature) preferably in the range of 100° C. to 200°C., for example, and a cold crystallization point (a heat dissipation start temperature) higher than the glass transition point and lower than the melting point and preferably in the range of 50° C. to 100° C., for example. As an example, the eutectic of mannitol, galactitol, and inositol (=0.557 mol: 0.273 mol: 0.206 mol) has a melting point of 150° C., a glass transition point of 16.1° C. at falling temperature, a glass transition point of 15.2° C. at rising temperature, a cold crystallization point of 72.8° C., a melting latent heat of 248 kJ/kg, and a cold crystallization latent heat of 157 KJ/kg. The eutectic mixture of mannitol, galactitol, and inositol in the glassy state can dissipate a large amount of latent heat by temporarily applying heat so as to be at about 90° C. in a part of the eutectic mixture.

Although cooling to −25° C. or lower is required to maintain the glassy state for about a year, cooling to the glassy state is not necessarily required to maintain the heat accumulation state of the material with the potential to undergo a phase transition to the glassy state. When cooled rapidly to about a room temperature (for example, about 40° C.), the material is solidified to be rubbery. This state can maintain the heat accumulation state. If the heat accumulation state can be maintained at about a room temperature, the low-temperature heat storage 21 does not need to be cooled during storage, thus greatly improving handling thereof.

As illustrated in FIG. 7, the heat supply system 20 further includes, in addition to the low-temperature heat accumulator 21 and the dissipated-heat collector 22, a melter 23 that melts the low-temperature PCM of the low-temperature heat accumulator 21, a rapid cooler 24 that rapidly cools the low temperature PCM, a storage warehouse 25 that stores the low-temperature heat accumulator 21, and a truck 26 that transports the low-temperature heat accumulator 21. In the heat supply system 20, the low-temperature heat accumulator 21 moves to the melter 23, the rapid cooler 24, the storage warehouse 25, the truck 26, and the dissipated-heat collector 22 in this order.

When using the low-temperature PCM with a melting point of 150° C., a glass transition point of 16.1° C. at falling temperature, and a cold crystallization point of 72.8° C. as an example, the melter 23 melts the low-temperature PCM with exhaust at 180° C. from the steam boiler 13a, and dissipates exhaust at 140° C. into the atmosphere. The rapid cooler 24 changes the low-temperature PCM in the molten state to the glassy state, which is the heat accumulation state, by rapidly cooling the low-temperature PCM. After storage and transportation of the low-temperature PCM in the glass state to heat-demanding areas, the dissipated-heat collector 22 generates latent heat from the low-temperature PCM by temporarily heating a part of the low-temperature PCM to be at a temperature higher than the cold crystallization point, for example, at about 90° C., thereby changing cold water at 20° C. to hot water in the range of 70° C. to 80° C.

The melter 23 is configured to be able to accommodate the low-temperature heat accumulator 21, and melts the low-temperature PCM of the low-temperature heat accumulator 21 using the exhaust from the steam boiler 13a. As illustrated in FIG. 8, the melter 23 includes a housing 23a that accommodates the low-temperature heat accumulator 21, and a pair of heat exchangers 23b that are disposed in the housing 23a so as to sandwich both side surfaces of the low-temperature heat accumulator 21 and heat the both side surfaces of the low-temperature heat accumulator 21 by heat transfer.

The forward and rearward of the housing 23a are open to allow movement of a cart 23e on which the low-temperature heat accumulator 21 is mounted. Each of the heat exchangers 23b is connected to an intake pipe 23c that is connected to the steam boiler 13a and supplies the exhaust from the steam boiler 13a, and an exhaust pipe 23d that discharges the exhaust after heat exchange.

Returning back to FIG. 7, the rapid cooler 24 is configured to be able to accommodate the low-temperature heat accumulator 21, and causes the low-temperature PCM in the molten state included in the low-temperature heat accumulator 21 to undergo a phase transition to the glassy state using the cooling pipes of the condenser 13e. The rapid cooler 24 is connected to the heat exchangers in which the cooling pipes of the condenser 13e are disposed, and cools the both side surfaces of the low-temperature heat accumulator 21 by heat transfer. The rapid cooler 24 has a configuration that is the same as or equivalent to the melter 23, except that the cooling water flows through the heat exchangers, for example.

The storage warehouse 25 stores the low-temperature heat accumulator 21 while maintaining the heat accumulation state, and the truck 26 transports the low-temperature heat accumulator 21 to a heat-demanding area while maintaining the heat accumulation state. To maintain the heat accumulation state of the low-temperature heat accumulator 21, it is sufficient that the temperature of the low-temperature heat accumulator 21 is suppressed to the glass transition point of the low-temperature PCM or lower. When accumulating heat in the low-temperature PCM that is solidified to be rubbery, installation of air conditioning equipment in the storage warehouse 25 and the truck 26 may be omitted.

The dissipated-heat collector 22 is configured to be able to dispose the low-temperature heat accumulator 21 therein, and induces cold crystallization of the low-temperature PCM by temporarily heating the low-temperature heat accumulator 21 to cause the low-temperature PCM to dissipate a large amount of latent heat. As illustrated in FIG. 9, the dissipated-heat collector 22 includes a housing 22a that accommodates the low-temperature heat accumulator 21, a heater 22b that is disposed in the housing 22a and temporarily heats a part of the low-temperature PCM of the low-temperature heat accumulator 21 to be at a higher temperature than the cold crystallization point, and a heat exchanger 22c that is disposed in the housing 22a and changes cold water supplied from the outside to hot water by transferring heat in contact with the low-temperature heat accumulator 21.

The housing 22a has a door through which the low-temperature heat accumulator 21 is inserted and removed. To accommodate the low-temperature heat accumulator 21 in the dissipated-heat collector 22, it is sufficient that a container lift is used, for example. The heater 22b is disposed in the housing 22a so as to be in contact with a bottom surface and a side surface of the low-temperature heat accumulator 21, for example. The heat exchanger 22c is disposed on the upper side in the housing 22a, for example. The components of the heat supply system 20 are as described above.

Next, procedures of a heat supply method according to the embodiment are described with reference to FIG. 10. Hereinafter, the low temperature PCM of the low temperature heat accumulator 21 before being disposed in the melter 23 is assumed to be in the crystalline state.

Firstly, the low-temperature heat accumulator 21 is disposed in the melter 23, and the low-temperature PCM of the low-temperature heat accumulator 21 is changed to the molten state using the exhaust from the steam boiler 13a (step S1). Specifically, as illustrated in FIG. 8, the low-temperature heat accumulator 21 is mounted on the cart 23e and then disposed in the melter 23, and the low-temperature PCM of the low-temperature heat accumulator 21 is melted by the heat exchangers 23b that has been heated by the exhaust from the steam boiler 13a.

Next, the low-temperature heat accumulator 21 that has been changed to the molten state in step S1 is disposed in the rapid cooler 24, and the low-temperature PCM of the low-temperature heat accumulator 21 is changed to the glassy state by rapidly cooling the low-temperature PCM using the cooling water of the condenser 13e (step S2). Specifically, the low-temperature heat accumulator 21 mounted on the cart 23e is disposed in the rapid cooler 24 that has a configuration equivalent to the melter 23 illustrated in FIG. 8, and the low-temperature PCM of the low-temperature heat accumulator 21 is rapidly cooled to the glass transition point or lower, thereby changing the low-temperature PCM to the glassy state via the supercooled liquid state.

Next, the low-temperature heat accumulator 21 that has been changed to the heat accumulation state in step S2 is stored in the storage warehouse 25 (step S3), and the low-temperature heat accumulator 21 is transferred to a heat-demanding area by the truck 26 at a timing when heat demand arises (step S4). The storage warehouse 25 and the truck 26 can maintain the heat accumulation state of the low-temperature PCM by maintaining the low-temperature PCM at the glass transition point or lower.

Next, the low-temperature heat accumulator 21 is disposed in the dissipated-heat collector 22 located in the heat-demanding area, and is caused to dissipate heat therefrom, thereby supplying heat to the heat-demanding area (step S5). Specifically, when a part of the low-temperature PCM in the glassy state is temporarily heated to be at the cold crystallization point or higher using the heater 26b as illustrated in FIG. 9, the low-temperature PCM is changed from the supercooled liquid state to the crystalline state via the cold crystalline state. Since the cold crystallization latent heat is dissipated at a time when cold crystallization proceeds, the heat exchanger 26c can collect the latent heat and change cold water at about 20° C. to hot water at about 70° C. to 80° C.

Next, the low-temperature heat accumulator 21 in the crystalline state is returned to the steam power generation plant 13 (step S6). The used low-temperature heat accumulator 21 may be returned to the installation location of the steam power generation plant 13 by the truck 26. The low-temperature heat accumulator 21 can be used as a heat source again by disposing the low-temperature heat accumulator 21 maintained in the crystalline state in the melter 23 again and repeating the same processes. The procedures of the heat supply method are as described above.

As described above, the Carnot battery 10 according to the embodiment includes the heat source device 11 that converts electric power into heat to generate hot air, the high-temperature heat accumulator 12 that is disposed downstream of the heat source device 11 and includes the PCM configured to receive the hot air supplied by the heat source device 11 to accumulate and dissipate heat, and the steam power generation plant 13 that is disposed downstream of the high-temperature heat accumulator 12 and collects heat from the hot air supplied by the high-temperature heat accumulator 12 to convert the heat into electric power. Thus, the large heat capacity of the high-temperature heat accumulator 12 can absorb short-period fluctuation in grid power that includes power derived from renewable energy. This allows stable conversion of grid power with large output fluctuation into generated power with small output fluctuation.

The heat supply system 1 according to the embodiment includes the Carnot battery 10, the low-temperature heat accumulator 21 that is configured to be attachable to and detachable from the steam power generation plant 13 of the Carnot battery 10 and includes the low-temperature PCM configured to collect and accumulate the heat discharged by the steam power generation plant 13, and the dissipated-heat collector 22 that is configured to be able to dispose the low-temperature heat accumulator 21 therein and collects heat dissipated by the low-temperature heat accumulator 21 to supply heat to heat-demanding areas. Thus, low-level thermal energy (excess heat) generated by the Carnot battery 10 can be collected to supply heat to heat-demanding areas. This can improve heat utilization efficiency of the energy storage system 1.

The present invention is not limited to the above embodiment, and modifications described below may be made.

Modified Examples

Although the heat source device 11 converts electric power into heat and the steam power generation plant 13 converts heat into electric power in the above embodiment, the present invention is not limited thereto. For example, a heat pump may be used for conversion of electric power into heat or conversion of heat into electric power.

Although the high-temperature heat accumulator 12 is formed such that the multiple passages through which air can pass are adjacent to each other and extend in the same direction in the above embodiment, the present invention is not limited thereto. The high-temperature heat accumulator 12 may have any shapes as long as heat exchange with the air is possible, for example, may be formed with a mesh structure.

Although the high-temperature heat accumulator 12 is formed by combining a large number of the spherical PCM capsules 12A in the above embodiment, the present invention is not limited thereto. The PCM capsules 12A may be formed in a block shape or a cylindrical shape, for example.

Although each of the PCM capsules 12A is formed to have a particle size in the range of 1 mm to 10 mm in the above embodiment, the present invention is not limited thereto. For example, the PCM capsules 12A may be formed as microparticles, with a particle size in the range of 1 μm to 1 mm, and the microparticle PCM capsules 12A may be placed into a mold and then bonded or sintered to form the high-temperature heat accumulator 12 in any shapes.

Although the exhaust from the steam boiler 13a is directly supplied to the melter 23 in the above embodiment, the present invention is not limited thereto. For example, a blower may be provided in the middle of the pipes connecting the steam boiler 13a and the melter 23 to feed the exhaust from the steam boiler 13a into the melter 23.

Although the low-temperature heat accumulator 21 accumulates heat using the 1 exhaust from the steam boiler 13a in the above embodiment, the present invention is not limited thereto. For example, the low-temperature heat accumulator 21 may accumulate heat by extracting air from the steam turbine 13c.

Although the container 21B that accommodates a large number of the PCM capsules 21A is formed in a cubic shape in the above embodiment, the present invention is not limited thereto. For example, the container 21B may be a container with a cylindrical shape and an internal space. In addition, as illustrated in FIG. 11, the container 21B may include a housing 21a and a pair of partition plates 21b that are disposed in the housing 21a and accommodate the PCM capsules 21A therebetween. Both ends of the housing 21a have through holes 21c through which air can pass, and the partition boards 21b have a large number of through holes 21d through which air can pass. Thus, heat can be accumulated in the PCM capsules 21A by directly venting the exhaust from the steam boiler 13a into the housing 21a via the through holes 21c.

Although the high-temperature heat accumulator 21 includes a large number of the spherical PCM capsules 21A in the above embodiment, the present invention is not limited thereto. The PCM capsules 21A may be formed in a block shape or a cylindrical shape, for example.

Although the container 21B accommodates a large number of the PCM capsules 21A in the above embodiment, the present invention is not limited thereto. A large number of the PCM capsules 21A may be joined to each other to form one low-temperature heat accumulator 21. In addition, although each of the PCM capsules 21A has a particle size in the range of 1 mm to 10 mm in the above embodiment, the present invention is not limited thereto. For example, the PCM capsules 21A may have a particle size in the range of 1 μm to 1 mm, and such minute PCM capsules 21A may be joined together to form the low-temperature heat accumulator 21 in any shapes.

Although the PCM with the potential to undergo a phase transition to the glassy state is used as the low-temperature PCM in the above embodiment, the present invention is not limited thereto. In a case where the low-temperature PCM does not need to be stored in the heat accumulation state for a long period of time, a PCM without the potential to undergo a phase transition to the glassy state may be used as the low-temperature PCM.

Although the melter 23 and the rapid cooler 24 are configured to heat or cool the both side surfaces of the low-temperature heat accumulator 21 while the low-temperature heat accumulator 21 is mounted on the cart 23e in the above embodiment, the present invention is not limited thereto. For example, the melter 23 may be configured to heat the low-temperature heat accumulator 21 from the lower side thereof using the heat exchanger disposed on the bottom surface in the housing 23a. In addition, the rapid cooler 24 may be configured to cool the low-temperature heat accumulator 21 from the upper side thereof using the heat exchanger disposed in the upper surface portion in a housing.

The above embodiment is merely an example, and should not be construed as limiting the present invention. Various modifications may be made without departing from the scope of the gist of the invention defined by the included claims. The components described in the embodiment and the modified examples may be freely combined. In addition, the present invention includes inventions equivalent to the invention defined by the included claims.

Industrial Applicability

The Carnot battery and the energy storage system of the present invention are useful as capable of stably supplying electric power of which output fluctuation derived from renewable energy is absorbed.

Reference Signs List

• • 1 Energy storage system
  • 10 Carnot battery
  • 11 Heat source device
  • 11b Blower
  • 12 High-temperature heat accumulator
  • 12A, 21A PCM capsule
  • 13 Steam power generation plant
  • 13a Steam boiler
  • 13c Steam turbine
  • 13e Condenser
  • 20 Heat supply system
  • 21 Low-temperature heat accumulator
  • 21B Container
  • 22 Dissipated-heat collector
  • 23 Melter
  • 24 Rapid cooler